So, what have we learned about specific genetic factors underlying heritability?
We've talked about two phenotypes in detail, schizophrenia and
now general cognitive ability.
We've found out a couple things.
First of all, and again, I'm going to return to this in the supplemental
lecture, the candidate-gene approach that really dominated
in behavioral genetics and psychiatric genetics for
almost 20 years has not really been particularly successful.
I don't want to par, completely dismiss the candidate-gene approach.
I think it's still a viable approach.
However, during that period of our,
of, of the history of our science, it didn't actually yield much.
Secondly, we are finding results with GWAS.
But when we're finding things with GWAS the affects are very very small,
therefore it takes massive sample sizes to find those effects.
And even with those massive sample sizes, a we, as we saw with height or
schizophrenia, we don't really identify all the relevant genetic variants.
Most of the var, most of the heritability is missing.
And one question that the field is grappling with, and
there's actually quite a bit of debate on this, and we'll come back to it actually
in the last week in this course, is whether or not it's worthwhile to invest
all these resources in identifying variants that have very small effects, and
account for a small portion of the varia, of the variants and the heritability.
The final thing is that, is that we, we've talked about is that behavioral phenotypes
aren't all that different coming out of GWAS as are physical phenotypes.
That is, just like physical phenotypes, the variants for phys,
psychological and psychiatric phenotypes are small and they, it, when we
accumulate all the ones we know about, still most of the variance is missing.